/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.xbean.classloader;

import java.util.Enumeration;
import java.util.LinkedList;
import java.util.List;
import java.util.NoSuchElementException;

/**
 * @version $Rev$ $Date$
 */
public final class UnionEnumeration implements Enumeration {
    private final LinkedList enumerations = new LinkedList();

    public UnionEnumeration(List enumerations) {
        this.enumerations.addAll(enumerations);
    }

    public UnionEnumeration(Enumeration first, Enumeration second) {
        if (first == null) throw new NullPointerException("first is null");
        if (second == null) throw new NullPointerException("second is null");

        enumerations.add(first);
        enumerations.add(second);
    }

    public boolean hasMoreElements() {
        while (!enumerations.isEmpty()) {
            Enumeration enumeration = (Enumeration) enumerations.getFirst();
            if (enumeration.hasMoreElements()) {
                return true;
            }
            enumerations.removeFirst();
        }
        return false;
    }

    public Object nextElement() {
        while (!enumerations.isEmpty()) {
            Enumeration enumeration = (Enumeration) enumerations.getFirst();
            if (enumeration.hasMoreElements()) {
                return enumeration.nextElement();
            }
            enumerations.removeFirst();
        }
        throw new NoSuchElementException();
    }
}
